Field of the Invention
The present invention relates to an intake throttle valve return device of engine that is to be used in a fuel injector or a carburetor.
FIG. 1 is a longitudinal sectional view showing a
prior-art intake throttle valve return device disclosed in for example Laid-Open Japanese Patent No. Sho 59-46345. In this drawing, numeral 1 denotes a carburetor body, and numeral 2 is a throttle valve securely fixed on a valve shaft 3. Numeral 4 designates a supporting arm fixed on the carburetor body 1, and numeral 5 is a bowl-shaped collar holder inserted and locked to support on the valve shaft 3, and is provided with a flange section 6. Numerals 7, 8 are cylindrical collars with a flange to receive an outer torsion spring 9; numerals 10, 11 are cylindrical collars having a flange for receiving the ends of an inner torsion spring 12; and numerals 13, 14 are cylindrical sleeves which are inserted and locked to support respectively on the valve shaft 3, and interposed between the above-mentioned cylindrical collars 7, 10 and between he cylindrical collars 8, 11, thereby preventing contact and interference between the aforementioned torsion springs 9, 12. Numeral 15 is a lock pin fixedly installed to the aforementioned carburetor body 1 for retaining the ends of torsion springs, and numeral 16 designates a throttle valve lever connected to the end of the valve shaft .
Either of the other end of the aforementioned torsion spring 9 and the other end of the torsion spring 12 inserted into the cylindrical sleeve 14 are locked at engaging portions 17, 17 formed on the above-mentioned throttle valve lever 16, and each one end is also locked on the above-described pin 15. Thus both the torsion springs 9 and 12 are wound around, and twisted into, the valve shaft 3 so that a spring force will act in the direction where the throttle valve 2 will be closed.
The above-mentioned bowl-shaped collar holder 5, as shown in the plane view of FIG. 2 and the side view of FIG. 3, has cutout ends 5a, 5b formed to hold the cutout section throughout the range of angle .alpha. corresponding to the angle of rotation of the valve shaft 3, and from this cutout section, one end of the inner torsion spring 12 is led outwardly, being locked on the pin 15.
The above-mentioned cylindrical sleeve 13 also, as shown in the sectional view of FIG. 4, are provided with cutout ends 13a and 13b formed to hold the cutout section throughout the range of angle corresponding to the angle of rotation of the valve shaft 3, and from this cutout section one end of the inner torsion spring 12 is led outwardly.
The valve shaft 3 described above, as shown in FIG. 4, has a cutout locking section 3a formed in parallel with the outer periphery, ranging from the supporting arm 4 portion to the shaft end, and the bowl-shaped collar holder 5 and the cylindrical sleeve 13 are provided with engaging holes 5c and 13c respectively which are formed to be engaged with this cutout locking section 3a.
The prior-art intake throttle valve return device, however, has the following problems.
(1) The bowl-shaped collar holder 5 and the cylindrical sleeve 13 have a wide cutout section so formed as to lead out one end of the inner torsion spring 12, resulting in a decrease in mechanical strength and difficulty in manufacture.
(2) Multiplication of parts are required.
(3) The valve shaft 3 has the cutout engaging section 3a formed from the supporting arm 4 position to the shaft end, resulting in decreased mechanical strength. To compensate for it, the shaft diameter has to be increased.
(4) Other ends of the torsion springs 9, 12 are led out in an axial direction and further bent in the circumferential direction. The cylindrical collar 11, the cylindrical sleeve 14 and the throttle valve lever 16 are provided with a circumferential long hole through which the end of the springs is inserted, on account of which, however, the mechanical strength of these parts is low.
(5) In assembling work, since the cylindrical sleeve 14 and the throttle valve lever 16 are fitted by the engaging section 17 to the other ends of the twisted torsion springs 9, 12 that have been led out, it is difficult to adjust the position in a circumferential direction of both for fitting them in the cutout engaging section at the end portion of the valve shaft 3 and accordingly to accomplish the assembling work.
(6) Other ends of the torsion spring 9, 12 are directly metallic-contacted with the engaging section of the cylindrical sleeve 14 and the throttle valve lever 16, and therefore it is likely that wear will occur due to abrasion resulting from displacement between both sides.
(7) The engaging section of the cylindrical collar 11, cylindrical sleeve 14 and throttle valve lever 16 for holding the other ends of the torsion springs 9, 12 has a long hole; in the assembling work, therefore, it is not easy to position and assemble the torsion springs 9, 12 in a twisted state.
(8) The flanged cylindrical collars 10, 11 which receive the torsion spring 12 is divided to both sides, and accordingly the torsion spring 12 is likely to move in a radial direction, and a part of the torsion spring 12 will bite in between both the cylinders, thereby interfering with operation.